Udugala-Ganehenege M Y, Heeg M J, Hryhorczuk L M, Wenger L E, Endicott J F
Department of Chemistry and Department of Physics, Wayne State University, Detroit, Michigan 48202, USA.
Inorg Chem. 2001 Mar 26;40(7):1614-25. doi: 10.1021/ic000726w.
The syntheses and donor-acceptor properties of some novel, halo-bridged dicopper(II) complexes of alpha,alpha'-bis(5,7-dimethyl-1,4,8,11-tetraazacyclotetradecane-6-yl)-o-xylene are reported. These complexes were characterized by their magnetic and electrochemical behavior, X-ray structure analysis, FAB mass spectroscopy, and electronic spectra. The bromo-bridged complex crystallized in the tetragonal system, space group P4(3)2(1)2, with a = 12.6584(5) A, c = 28.6483 (14) A, Z = 4, R = 0.071, and Rw = 0.147. The chloro-bridged complex crystallized in the monoclinic system, space group C2/c, with a = 32.749(2) A, b = 18.8915(9) A, c = 26.022(2) A, beta =114.831 degrees, Z = 12, R = 0.080, and Rw = 0.132. Both molecules have C2 symmetry. The two copper(II) ions are axially bridged by a bromine or a chlorine, and the two macrocycles are bridged by an o-xylene group. Each complex displays a cofacial ring arrangement. The Cu-X distance (where X = Cl, Br) is shorter than the sum of van der Waals radii of Cu and X. The phenyl ring is approximately orthogonal to the Cu-X-Cu axis. The nonhalo-bridged complex has a significant affinity for halides (Kf approximately 10(4) M(-1)). The chloride-bridged complex had barely resolved differential pulse polarographic waves (DeltaE1/2 approximately 28 mV), while the bromide-bridged complex exhibited two CV waves in the 1.0-1.5 V range (DeltaE1/2 = 0.24 V). All the Cu(II)/Cu(I) couples were irreversible with a cathodic peak at about - 0.9 V. The magnetic susceptibility results below 20 K follow Curie-Weiss behavior, indicating that the magnetic interaction between the two Cu centers is weakly antiferromagnetic with J < or = -1 cm(-1) for all three complexes. A bridging-ligand-mediated superexchange model is used to treat the magnetic and electron-transfer coupling in the Cu(II)(X-)Cu(II) complexes. A single set of perturbation theory parameters is consistent with the magnetic and electrochemical observations on the chloride-bridged complex and the magnetic properties of the bromide-bridged complex. The electrochemical behavior of the latter suggests a relatively low-energy, high-spin configuration for the Cu(III)(Br-)Cu(II) complex. The analysis attributes the weak Cu(II)/Cu(II) coupling to the orthogonality of the donor and acceptor orbitals to the bridging axis. It is inferred that bridging halide-mediated metal-metal dsigma/psigma coupling significantly alters the chemical properties of the bimetallic complexes only when the donor and acceptor orbitals are coaxial with the bridging ligand. In such a limit, the coupling takes the form of a three-center bonding contribution.
报道了一些新型的α,α'-双(5,7-二甲基-1,4,8,11-四氮杂环十四烷-6-基)-邻二甲苯的卤桥联二铜(II)配合物的合成及其给体-受体性质。通过它们的磁性和电化学行为、X射线结构分析、快原子轰击质谱和电子光谱对这些配合物进行了表征。溴桥联配合物在四方晶系中结晶，空间群为P4(3)2(1)2，a = 12.6584(5) Å，c = 28.6483 (14) Å，Z = 4，R = 0.071，Rw = 0.147。氯桥联配合物在单斜晶系中结晶，空间群为C2/c，a = 32.749(2) Å，b = 18.8915(9) Å，c = 26.022(2) Å，β = 114.831°，Z = 12，R = 0.080，Rw = 0.132。两个分子都具有C2对称性。两个铜(II)离子通过一个溴或一个氯轴向桥联，两个大环通过一个邻二甲苯基团桥联。每个配合物都呈现出共面环排列。Cu-X距离（其中X = Cl、Br）短于Cu和X的范德华半径之和。苯环近似垂直于Cu-X-Cu轴。非卤桥联配合物对卤化物具有显著的亲和力（Kf约为10(4) M(-1)）。氯桥联配合物的差分脉冲极谱波几乎无法分辨（ΔE1/2约为28 mV），而溴桥联配合物在1.0 - 1.5 V范围内呈现出两个循环伏安波（ΔE1/2 = 0.24 V）。所有的Cu(II)/Cu(I)电对都是不可逆的，在约 - 0.9 V处有一个阴极峰。低于20 K时的磁化率结果遵循居里-外斯行为，表明对于所有三种配合物，两个Cu中心之间的磁相互作用是弱反铁磁性的，J ≤ -1 cm(-1)。采用桥联配体介导的超交换模型来处理Cu(II)(X-)Cu(II)配合物中的磁和电子转移耦合。一组单一的微扰理论参数与氯桥联配合物的磁和电化学观测结果以及溴桥联配合物的磁性性质一致。后者的电化学行为表明Cu(III)(Br-)Cu(II)配合物具有相对低能量、高自旋的构型。分析将弱的Cu(II)/Cu(II)耦合归因于给体和受体轨道相对于桥联轴的正交性。据推断，仅当给体和受体轨道与桥联配体同轴时，桥联卤化物介导的金属-金属dsigma/psigma耦合才会显著改变双金属配合物的化学性质。在这种极限情况下，耦合采取三中心键合贡献的形式。
